Trinuclear {Sr[UO2L3]2(H2O)4} and pentanuclear {Sr[UO2L3]4}2− uranyl monocarboxylate complexes (L-acetate or n-butyrate ion)†
Abstract
Crystals of two acetate complexes, Cs2{Sr[UO2L3]4} (1) and [Sr(H2O)6][UO2L3]2{Sr(H2O)4[UO2L3]2}2 (2), and one n-butyrate complex, {Sr(H2O)4[UO2L3]2}·2H2O (3), of uranium(VI), where L is a corresponding monocarboxylate ion, were studied by means of FTIR spectroscopy and single crystal X-ray analysis. The structure of 1 contains pentanuclear anionic complexes, {Sr[UO2L3]4}2−, bonded in a three dimensional framework by electrostatic interactions with Cs+ cations. The structure of 2, in addition to ‘typical’ uranyl triacetate complexes of [UO2L3]− and [Sr(H2O)6]2+ cations, contains neutral trinuclear complexes, {Sr(H2O)4[UO2L3]2}. The structure of 3 with n-butyrate ions consists of neutral complexes of {Sr(H2O)4[UO2L3]2} and molecules of crystallized water. Analysis of intermolecular interactions in 2 and 3 by means of two independent approaches (molecular Voronoi–Dirichlet polyhedra and molecular Hirshfeld surfaces) revealed that discrete complex groups are connected with one another mostly due to H/O hydrogen bonds and H/H dispersion interactions. A dynamic balance among mono- and poly-nuclear complexes in aqueous solutions containing R2+ and [UO2L3]− ions is proposed. The effect of the alkyl chain and the nature of the R2+ cation on the balance is discussed.